Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-07-17
2004-04-06
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C427S002140, C427S162000, C427S164000, C427S212000, C427S213300
Reexamination Certificate
active
06716526
ABSTRACT:
This invention relates to particulate compositions comprising a core of hydrophobic material within a shell of polymeric material and a process of producing said compositions. The invention also relates to novel articles comprising said compositions and in particular novel fibres comprising said compositions and a process for making said fibres. In the invention the core may comprise an active ingredient such as ultra violet (UV) absorbers, flame retardants or phase change substances. Desirably the particulate compositions can easily be incorporated into a variety of products such as coatings, sun-screens or a variety of textile products.
There are many instances where it would be desirable to provide capsules comprising a shell surrounding a core material. For instance the core may comprise an active ingredient which is released slowly, such as fragrances, pesticides, medicaments and the like. In other instances it may be desirable for the core material encapsulated within the shell to remain substantially intact either permanently or at least until a suitable trigger induces the core to be released. There are instances where it is important that the core material is not released from the capsules. This includes for example encapsulated ultra violet light absorbers for use in sunscreens and articles of clothing.
Another important application includes encapsulated phase change materials which can be used as thermal energy storage products. Such products include fabrics and especially clothing. Of particular value are for example microcapsules comprising a phase change hydrocarbon material which are combined with a fibre spinning dope, which is then extruded to form filaments which are cured and then collected. Since the spinning process normally requires passing the extruded dope into an environment at temperatures often in excess of say 150 or 200° C. and can be even as high as 350° C. or higher, it is desirable for substantially all of the core material to be retained in the shell. Fibres such as nylon and polyester fibres are produced by melt spun process, which generally involves very high temperatures, for instance in excess of 300 or 350° C. However, it is difficult to find the right chemistry that provides an impervious, durable shell wall that can be incorporated into fibres, without suffering deleterious effects during the spinning process.
Various methods for making capsules have been proposed in the literature. For instance it is known to encapsulate hydrophobic liquids by dispersing the hydrophobic liquid into an aqueous medium containing a melamine formaldehyde pre-condensate and then reducing the pH resulting in an impervious aminoplast resin shell wall surrounding the hydrophobic liquid. Variations of this type of process are described in GB-A-2073132, AU-A-27028/88 and GB-A-1507739, in which the capsules are preferably used to provide encapsulated inks for use in pressure sensitive carbonless copy paper.
However, although capsules based on melamine formaldehyde resins are both impervious and durable, they tend to suffer the disadvantage that they are less impermeable at elevated temperatures. In addition there is also a risk that at elevated temperatures formaldehyde is evolved.
WO-A-9924525 describes microcapsules containing as a core a lipophilic latent heat storage material with a phase transition at −20 to 120° C. The capsules are formed by polymerizing 30 to 100 wt. % C
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alkyl ester of (meth)acrylic acid, up to 80 wt. % of a di- or multifunctional monomer and up to 40 wt. % of other monomers. The microcapsules are said to be used in mineral molded articles. However, the specific polymer compositions described would not be suitable for exposure to high temperatures since the lipophilic phase change material would be very quickly lost.
There exists a need for particles that comprise a substantially impervious shell wall that retains a hydrophobic material, especially at elevated temperatures. There is a particular need to provide such particles that do not release the core material even when exposed to the harsh conditions, for instance high temperature, high pressures and shearing conditions of producing synthetic fibres.
There also exists a need for particles that do not release the core material until there has been a suitable release trigger, for instance pH. Nevertheless, the core material would not be released in the absence of the trigger. There is also a need to achieve all of these objectives but avoiding the use of formaldehyde condensation products.
Thus according to the present invention we provide a composition comprising particles which comprise a core material within a polymeric shell, wherein the core material comprises a hydrophobic substance, characterized in that the polymeric shell comprises a copolymer formed from a monomer blend which comprises,
A) 30 to 90% by weight methacrylic acid
B) 10 to 70% by weight alkyl ester of (meth)acrylic acid which is capable of forming a homopolymer of glass transition temperature in excess of 60° C. and
C) 0 to 40% by weight other ethylenically unsaturated monomer.
Also included in the present invention is a process of manufacturing a composition comprising particles which comprise a core material within a polymeric shell, wherein the core material comprises a hydrophobic substance, comprising the steps,
1) forming a solution of monomer in the hydrophobic liquid,
2) homogenising the monomer solution into an aqueous phase to form an emulsion,
3) subjecting the emulsion to polymerization conditions, and
4) forming a dispersion of polymeric particles in the aqueous phase characterized in that the polymeric shell comprises a copolymer formed from a monomer blend which comprises,
A) 30 to 90% by weight methacrylic acid
B) 10 to 70% by weight alkyl ester of (meth)acrylic acid which is capable of forming a homopolymer of glass transition temperature in excess of 60° C. and
C) 0 to 40% by weight other ethylenically unsaturated monomer.
The process may employ an emulsifying system, for instance emulsifiers, other surfactants and/or polymerization stabilizers. Thus in a preferred form of the invention an emulsifier, which may have a high HLB is dissolved into water prior to emulsification of the monomer solution. Alternatively the monomer solution may be emulsified into water with a polymerization stabilizer dissolved therein. The polymerisation stabiliser can be a hydrophilic polymer, for example a polymer containing pendant hydroxyl groups, for instance a polyvinyl alcohol and hydroxyethylcellulose. Generally it is preferred to use polyvinyl alcohol which has been derived from polyvinyl acetate, wherein between 85 and 95%, preferably 90% of the vinyl acetate groups have been hydrolysed to vinyl alcohol units. The polymerisation step may be effected by subjecting the aqueous monomer solution to any conventional polymerisation conditions. Generally polymerisation is effected by the use of suitable initiator compounds. Desirably this may be achieved by the use of redox initiators and/or thermal initiators. Typically redox initiators include a reducing agent such as sodium sulphite, sulphur dioxide and an oxidising compound such as ammonium persulphate or a suitable peroxy compound, such as tertiary butyl hydroperoxide etc. Redox initiation may employ up to 1000 ppm, typically in the range 1 to 100 ppm, normally in the range 4 to 50 ppm.
Preferably the polymerisation step is effected by employing a thermal initiator alone or in combination with other initiator systems, for instance redox initiators. Thermal initiators would include any suitable initiator compound that releases radicals at an elevated temperature, for instance azo compounds, such as azobisisobutyronitrile (AZDN), 4,4′-azobis-(4-cyanovalereic acid) (ACVA) or t-butyl perpivilate. Typically thermal initiators are used in an amount of up 50,000 ppm, based on weight of monomer. In most cases, however, thermal initiators are used in the range 5,000 to 15,000 ppm, preferably around 10,000 ppm. Preferably a suitable thermal initiator with
Dungworth Howard Roger
Weston Rachel Clare
Ciba Specialty Chemicals Water Treatments Ltd.
Seidleck James J.
Stevenson Tyler A.
Tran Thao
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